The invention relates to an oscillation damper of the type having a working piston that is disposed in a damper tube that is at least partially filled with a damping liquid.
An oscillation damper of this general type is disclosed, for example, in European patent document EP 1 538 366 A1. In this known oscillation damper, two electromagnetic control valves are provided which are disposed hydraulically in parallel with the working piston, one which one has a flow passing through it only when the piston rod performs a retraction movement, with the other having a flow passing through it only when the piston rod performs an extension movement. The electromagnetic control valves are formed as so-called backpack valves; i.e., they are disposed in housings which are flanged to the damper tube of the oscillation damper.
The damping force can be continuously varied by the two electromagnetic control valves. In the case of the known oscillation damper, the damping forces can thus be continuously varied independently of each other in the traction stage and in the compression stage of the oscillation damper.
A disadvantage of this known oscillation damper is that each damping valve requires two connection bores in order to ensure the necessary inflow and outflow of the damping liquid. As a consequence, a total of four connection bores are to be introduced into the damper tube, which is complex in terms of manufacturing technology and causes the damper tube to weaken. Furthermore, in the known oscillation damper two independent housings are provided, wherein one damping valve is disposed in each housing. By arranging two damping valves in separate housings on the outer circumference of the damper tube, the oscillation damper requires on the whole a considerable amount of installation space which is not available in all vehicles to the chassis frame design engineers. The applicability of the known oscillation damper is thus restricted.
One object of the invention, therefore, is to provide an oscillation damper of the type described above, which obviates the described disadvantages.
This and other objects and advantages are achieved by the oscillation damper according to the invention, in which both damping valves are disposed in a common housing having a first and a second hydraulic chamber. The first hydraulic chamber is connected via a first bore to the working chamber remote from the piston rod and the second hydraulic chamber is connected via a second bore to the working chamber on the piston rod-side. A flow guiding element separates the two hydraulic chambers from one another, such that the damping liquid flowing into the first hydraulic chamber when the piston rod performs a retraction movement is supplied to the first damping valve in the valve through-flow direction, and the damping liquid flowing into the second hydraulic chamber when the piston rod performs an extension movement is supplied to the second damping valve in the valve through-flow direction.
The inventive arrangement of the damping valves in a single housing ensures that in comparison with the solution disclosed in European patent document EP 1 538 366 A1, a considerably smaller amount of installation space is required for the purpose of accommodating the oscillation damper. As a consequence, it is possible to utilize the oscillation damper according to the invention in vehicles in which oscillation dampers having only a single backpack valve have hitherto been used. In the case of vehicle chassis frames which provide only a small amount of installation space for the oscillation damper, the inventive arrangement of the two damping valves in a single housing can ensure a separate damping adjustment in the traction stage and in the compression stage of the oscillation damper in spite of the small installation space.
It is also advantageous that the oscillation damper in accordance with the invention requires only two connection bores to connect the housing to the damper tube inner space. Therefore, the inventive housing can be connected to the damper tube inner space merely via two connection bores because, due to the arrangement of the flow guiding element, during a retraction movement of the piston rod the first hydraulic chamber forms an inflow chamber and the second hydraulic chamber forms an outflow chamber for the damping liquid. In a similar manner, the arrangement of the flow guiding element ensures that during an extension movement of the piston rod the second hydraulic chamber forms an inflow chamber and the first hydraulic chamber forms an outflow chamber for the damping liquid. Therefore, with the oscillation damper in accordance with the invention, both hydraulic chambers can essentially be both the outflow chamber and also the inflow chamber, depending on the movement direction in which the piston rod and the working piston attached thereto move (traction direction or compression direction).
In accordance with the invention, the damping valves are formed preferably as electromagnetically operable, continuously adjustable control valves. The basic structure of damping valves of this type is already known from European patent document EP 1 538 366 A1 (above). The damping liquid must flow against these damping valves centrally in the middle. This central middle flow against the damping valves is ensured by means of the inventive flow guiding element for both valves, i.e., for both movement directions of the piston rod.
In the continuously adjustable damping valves, the damping force is generated by virtue of the fact that the hollow-cylindrical adjusting gate valve is displaced along its longitudinal axis on the cylindrical part of the deflection element, through which a flow can pass and with which the adjusting gate valve cooperates. By the axial displacement of the adjusting gate valve, a throttling opening disposed in the cylindrical part of the deflection element is revealed to a greater or lesser extent so that, depending upon the position of the adjusting gate valve, this throttle opening provides a certain degree of flow resistance for the damping liquid.
Basically, in the oscillation damper in accordance with the invention it is sufficient to provide only the continuously adjustable damping valves. However, in order to achieve damping which satisfies the requirements of driving comfort, it can be expedient to connect an additional passive valve element into the flow path in a hydraulic manner upstream of the active (adjustable) valve element which is formed by the adjusting gate valve and the cylindrical part of the deflection element. Depending upon the design of this additional passive valve element, the damping force progression can be influenced in a desired manner, and can be adapted e.g., to specific manufacturer specifications or wishes.
The flow guiding element can be produced essentially from different materials. Cost-effective production can be achieved if the flow guiding element is formed as a pressed sheet metal part or as a sintered component. However, it is also possible to produce the flow guiding element from synthetic material. In this case, the synthetic material injection molding method can be deployed for producing the flow guiding element.
In a preferred embodiment of the invention, the housing in which the damping valves are disposed is cylindrical. In this case, it is possible in a particularly simple manner to dispose the damping valves coaxially with respect to each other in the housing, and also the circular disk-shaped flow guiding element can be disposed conveniently, coaxial with respect to the damping valves and between same.
To permit installation of the entire arrangement of the two damping valves and the flow guiding element that is disposed therebetween, securely and firmly in the housing, the latter can comprise a shoulder which protrudes radially towards them and on which the flow guiding element is supported. In order to seal the first hydraulic chamber with respect to the second hydraulic chamber, a seal can be disposed in an advantageous manner between the radial shoulder of the housing and the flow guiding element. This seal can be formed as a simple 0-ring seal.
However, the radial shoulder can also alternatively be dispensed with and the flow guiding element can be sealed on its outer circumference against the cylindrical inner wall of the housing.
In accordance with the above-described embodiment of the invention, the sole objective of the flow guiding element is to supply the damping liquid to the respective damping valve, without a damping force being generated when a flow passes through the flow guiding element. However, in accordance with another embodiment of the invention, the flow guiding element is already equipped with pressure limiting valves which (as seen in the through-flow direction) are connected hydraulically upstream of the damping valves, which in turn are disposed hydraulically in parallel with the working piston. Therefore, the flow guiding element has a dual function: on the one hand it supplies the damping liquid to the respective damping valve, and on the other hand it actually generates a damping force which influences the damping characteristic. For this purpose, the flow guiding element comprises at least two channels to allow damping liquid to flow through, and the flow guiding element has pressure limiting valves disposed on it, wherein one pressure limiting valve can be influenced by damping liquid which flows through one channel and the other pressure limiting valve can be influenced by damping liquid which flows through the other channel. In a preferred manner, the pressure limiting valves disposed on the flow guiding element are formed as disk valves, in particular pretensioned disk valves.
In a preferred embodiment of the invention, each of the damping valves comprises a passive valve element in the form of a pressure limiting valve, and the additional pressure limiting valves which are disposed on the flow guiding element and generate a damping force are connected in a hydraulic manner upstream of these passive valve elements. Therefore, in the case of this embodiment two passive valve elements are each connected hydraulically in series one behind the other, in both through-flow directions. The two passive valve elements which are connected one behind the other in series preferably have different opening pressures.
In accordance with the invention, each of the first and the second damping valves comprises a non-return valve, to ensure that the damping liquid flows through the first damping valve only when the piston rod performs a retraction movement, and that the damping liquid flows through the second damping valve only when the piston rod performs an extension movement. In a preferred manner, each continuously adjustable damping valve comprises a passive valve element which in the valve through-flow direction is connected hydraulically upstream of the control valve, wherein as seen in the through-flow direction a non-return valve is connected hydraulically upstream of each passive element. These non-return valves can be formed as simple disk valves which do not generate any noteworthy damping force when a flow passes through them. By virtue of these non-return valves, the damping liquid is prevented from flowing through the damping valves in the respective undesired directions, when the control valves are open.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.